This invention relates to magnetically levitated vehicle (maglev) and propulsion systems and more particularly to maglev systems in which "FIG. 8" coils or windings are mounted on vertical walls to provide suspension, lateral guidance, and propulsion for the vehicle. The invention further includes changes in the coil patterns to provide propulsion when the vehicle coil is symmetrically placed about the horizontal midplane of the "FIG. 8" coil. In addition, the invention provides for changing the spacing between the upper and lower coil whereby increasing the spacing between the upper and lower loops of the "FIG. 8" coil provides one with the capability to partially control the stable range of vertical suspension and to partially control the vehicle suspension stiffness.
Maglev development began more than two decades ago in the United States, Germany, Japan, Canada and England. In the United States, renewed interest has been directed toward magnetic levitation transportation systems in view of such factors as energy conservation, high speed transportation at ground level, economic and environmental problems associated with conventional systems, and competition from West Germany, and Japan.
The use of an electrodynamic suspension to provide levitation in maglev systems is well known in the prior art (see further, U.S. Pat. No. 3,470,828, issued Oct. 7, 1969, to Powell et al). A number of methods of using magnetic forces to suspend, guide, and propel vehicles have been described in the literature. There are two basic suspension concepts that are based on the use of magnetic forces. One called the Electromagnetic System (EMS) utilizes the attractive force between controlled d.c. electromagnets and ferromagnetic rails while the other called the Electrodynamic System (EDS) utilizes the repulsive force between eddy currents induced in non-ferromagnetic metal conductors and superconducting magnets (SCM's) operating in the persistent current mode and moving relative to the conductors. Generally, the SCM's or the electromagnets are mounted on the lower part of the vehicle, while the iron rails or non-ferromagnetic metal conductors are mounted on the fixed guideway. The propulsion system most frequently used for either the EMS or EDS suspension is the linear synchronous motor (LSM). The LSM consists of windings placed on the guideway that are energized by an external source of three phase or multiphase power. The 3-phase or, in the alternative, multiphase excitation of the windings produces a traveling magnetic wave that interacts with the onboard magnets and moves the vehicle along the guideway at a synchronous speed, a speed equal to that of the traveling magnetic wave.
The repulsive levitation, suspension, force is generated by the interaction between a rapidly changing magnetic field generated by superconducting magnets aboard the moving vehicle and eddy currents induced in the guideway conductor. The guideway conductor can be made of a continuous sheet of a non-magnetic conductor, such as aluminum, or of discrete coils, loops or slotted hollow tubular type structures of similar material.
A special suspension concept that is based on the EDS is called "null-flux" suspension. It was invented by J. Powell and G. Danby in the late sixties and patented in 1969, see U.S. Pat. No. 3,470,828, as referred to above. The concept was invented as a way to reduce the electromagnetic drag force that is inherent in any suspension system that relies on eddy currents in the conductors. The concept also results in a stiffer suspension system than non-null-flux approaches. The heart of the null-flux system is a series of shorted "FIG.-8" coils. The "FIG.-8" coils may be vertically oriented on the guideway or folded over so that the upper and lower loops of the "FIG.-8" are parallel to each other. When an energized coil, for example an SCM, passes midway between the loops, no net current is induced in the loops because they are cross connected or counter wound hence the term "null-flux". When the SCM is displaced from the midplane or neutral position relative to the upper and lower loops, a large net current is induced in the loops and a strong repulsive force acts to restore the SCM to the neutral or "null-flux" position. Some maglev design concepts utilize the same vehicle magnets to perform more than one of the basic functions, suspension, guidance, or propulsion. This multiple tasking occurs when the vehicle magnets interact with suitable guideway mounted devices. Some additional concepts, as described in the literature, also include multi-use guideway-mounted coils. For example, the Japanese "Linear Motor Car" developed at the Japanese Railway Technical Research Institute and currently being tested at the Miyazaki Test Track applies externally excited three phase power to a set of vertically-mounted guideway coils for lateral guidance and for propulsion of the vehicle. A Canadian conceptual design also uses such a set of dual purpose, guidance and propulsion, coils mounted on the guideway. In both designs, a separate set of guideway-mounted coils is used for suspension. In addition, both concepts require that the propulsion and guidance coils mounted on opposite vertical walls must be cross-connected to provide lateral, null-flux guidance.
In the invention described herein, the vehicle-borne magnets interact with a single set of coils mounted on vertical guideway walls to produce a form of "null-flux" suspension, lateral guidance, and when the guideway mounted coils are excited with multi-phase power from an external source, propulsion as well. The lateral guidance is not of the "null-flux" type and does not require cross-connecting of coils mounted on opposite sides of the walls of the guideway. The lateral guidance forces arise naturally in this invention because of the interaction of the field from the vehicle-borne SCM's with the eddy currents induced in the "FIG.-8" coils producing both a vertical force component for the suspension, and a force normal, horizontal, to the coil plane for lateral guidance.
It is an object of this invention to employ a "FIG. 8" coil system attached to the guideway to provide suspension and lateral guidance to a SCM equipped vehicle.
It is a further object of this invention to longitudinally offset one loop of the "FIG. 8" coil from the other loop to provide propulsion as well as suspension and lateral guidance to a SCM equipped vehicle.
Another object of this invention provides for altering the spacing between the loops of the "FIG. 8" coil to partially control the vertical stability range and the vertical suspension stiffness.
Additional advantages, objects and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.